ABSTRACT All‐perovskite tandem solar cells (APTSCs) emerge as promising low‐cost and high‐efficiency next‐generation photovoltaics. To further increase the power conversion efficiencies (PCEs), a deeper understanding and fine‐tuned optimization of the optics is required, since most reports fall below 90% of the theoretical limit in photocurrent. Here, we demonstrate a synergistic multi‐faceted approach to overcome the optical constraints: incorporation of front‐sided nanotextures into APTSCs yields a broadband improvement of light in‐coupling, which eliminates thin‐film interference effects in reflectance, equivalent to a gain of 0.45 mA∙cm −2 in photocurrent. On the material level, parasitic absorption is reduced by optimizing the front ITO layer and replacing PEDOT:PSS for the bottom subcell with a graphene oxide/self‐assembled monolayer (GO/SAM) bilayer, improving the overall current gain to 1 mA∙cm −2 in each subcell. The resulting APTSC achieves a power conversion efficiency (PCE) of 27.98% with a short‐circuit current density ( J SC ) of 17.18 mA∙cm −2 , one of the highest reported values for this technology to date. Through comprehensive optical simulations, we explore the optical potential of APTSCs and further highlight upper limits of the subcell photocurrents in various tandem architectures. This work provides experimental and theoretical insights into optical optimization routes to increase the PCE of APTSCs well beyond 30%.

Despite rapid advances in all-perovskite multi-junction devices, the prevalent hole-transport layer (HTL), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), constrains stability and efficiency in narrow-band-gap tin-lead (Sn-Pb) bottom cells due to acidity and parasitic absorption. Although self-assembled monolayers (SAMs) are well established as HTLs in Pb perovskites and therefore considered promising for Sn-Pb perovskites, their implementation is lagging behind. In this study, we uncover the underlying mechanism by which SAMs limit charge extraction and induce non-uniform buried interfaces in Sn-Pb perovskite films. Guided by these insights, we demonstrate that a graphene oxide/SAM bilayer concurrently mitigates electronic and ionic losses, enabling 22.1% single-junction Sn-Pb efficiency with a 0.88 V open-circuit voltage. In all-perovskite triple-junctions, the bilayer reduces parasitic absorption losses in the near-infrared, yielding 27.3% efficiency (stabilized at 27.0%). The bilayer’s chemically benign nature improved device stability, retaining 90% of initial efficiency after 770 h of operation at 25°C.

The stability of perovskite-based tandem solar cells (TSCs) is the last major scientific/technical challenge to be overcome before commercialization. Understanding the impact of mobile ions on the TSC performance is key to minimizing degradation. Here, a comprehensive study that combines an experimental analysis of ionic losses in Si/perovskite and all-perovskite TSCs using scan-rate-dependent current-voltage (J-V) measurements with drift-diffusion simulations is presented. The findings demonstrate that mobile ions have a significant influence on the tandem cell performance lowering the ion-freeze power conversion efficiency from >31% for Si/perovskite and >30% for all-perovskite tandems to approximate to 28% in steady-state. Moreover, the ions cause a substantial hysteresis in Si/perovskite TSCs at high scan speeds (400 s(-1)), and significantly influence the performance degradation of both devices through internal field screening. Additionally, for all-perovskite tandems, subcell-dominated J-V characterization reveals more pronounced ionic losses in the wide-bandgap subcell during aging, which is attributed to its tendency for halide segregation. This work provides valuable insights into ionic losses in perovskite-based TSCs which helps to separate ion migration-related degradation modes from other degradation mechanisms and guides targeted interventions for enhanced subcell efficiency and stability.

Typically, the perovskite top-cell processes of monolithically integrated perovskite/silicon tandem solar cells (PSTSCs) include a slow and expensive atomic layer deposition (ALD) to grow a tin oxide (SnOx) buffer layer protecting against sputter damage during the subsequent transparent top electrode deposition. We successfully replaced the ALD-SnOx buffer layer with industry-compatible thermal evaporation of bathocuproine (BCP). By applying soft-sputter deposition of indium zinc oxide (IZO), we circumvent the increased risk of sputter damage when replacing ALD-SnOx with organic BCP. In addition to technological advantages, this leads to a 20 mV gain in open-circuit voltage, similar charge extraction rates, and higher current densities due to less parasitic absorption, as confirmed by absolute and transient photoluminescence, current density-voltage, spectral responsivity, and transient surface photovoltage measurements. Integrating the BCP/IZO top contact into tandem solar cells enables a certified power conversion efficiency of 29.91% of our ALD-free PSTSC using industrial silicon bottom cells from Q CELLS' Q.ANTUM technology.

The front electrode of monolithically integrated perovskite/silicon tandem solar cells commonly consists of a transparent conductive oxide (TCO). TCOs are usually deposited using the well-established method of magnetron sputtering. High particle energies, however, can cause sputter damage to sensitive substrates during the deposition process. Therefore, a SnO 2 buffer layer is used in all current perovskite top-cell designs with p-i-n polarity and competitive efficiencies. Here, we propose a methodology to identify electrical losses in perovskite solar cells (PSC) caused by sputter damage during the TCO deposition. We also show a simple method for minimizing sputter damage to the PSC, which enables SnO 2 buffer layer-free devices. Evaluation of the ideality factor and pseudo-current density-voltage (J-V) curves, reconstructed from light intensity-dependent J-V measurements on tandem top-cell-equivalent semi-transparent single-junction PSCs, revealed that sputter damage causes transport and non-radiative recombination losses. These losses result in a lower open-circuit voltage (VOC) and fill factor (FF), limiting the PSC performance. By lowering the sputter power density, we reduced the impact of sputter damage. This resulted in improved VOCs (~13 m V) and FFs (-3%) of the semi-transparent PSCs, which is a direct consequence of the reduced electrical losses [1]. Finally, we applied our low-damage sputter approach on SnO 2 buffer layer-free monolithic perovskite/silicon tandem devices. Compared to tandem devices with a SnO 2 buffer layer, the SnO 2 buffer layer-free devices were optically superior, resulting in a device current density improvement of 0.52 mA/cm 2 due to increased current densities in both sub-cells[1]. This is an important development for further optical performance optimization of tandem devices. [1] M. Hartel et al., ‘Reducing sputter damage-induced recombination losses during deposition of the transparent front-electrode for monolithic perovskite/silicon tandem solar cells', vol. 252, no. October 2022, pp. 1-7, 2023, doi: 10.1016/j.solmat.2023.112180.

Achieving high solar-to-hydrogen (STH) efficiency concomitant with long-term durability using low-cost, scalable photo-absorbers is a long-standing challenge. Here we report the design and fabrication of a conductive adhesive-barrier (CAB) that translates >99% of photoelectric power to chemical reactions. The CAB enables halide perovskite-based photoelectrochemical cells with two different architectures that exhibit record STH efficiencies. The first, a co-planar photocathode-photoanode architecture, achieved an STH efficiency of 13.4% and 16.3 h to t 60 , solely limited by the hygroscopic hole transport layer in the n-i-p device. The second was formed using a monolithic stacked silicon-perovskite tandem, with a peak STH efficiency of 20.8% and 102 h of continuous operation before t 60 under AM 1.5G illumination. These advances will lead to efficient, durable, and low-cost solar-driven water-splitting technology with multifunctional barriers.

Improved stability and efficiency of two-terminal monolithic perovskite-silicon tandem solar cells will require reductions in recombination losses. By combining a triple-halide perovskite (1.68 electron volt bandgap) with a piperazinium iodide interfacial modification, we improved the band alignment, reduced nonradiative recombination losses, and enhanced charge extraction at the electron-selective contact. Solar cells showed open-circuit voltages of up to 1.28 volts in p-i-n single junctions and 2.00 volts in perovskite-silicon tandem solar cells. The tandem cells achieve certified power conversion efficiencies of up to 32.5%.

Many research groups work on overcoming the 30% power conversion efficiency (PCE) level for perovskite/ silicon tandem solar cells with various approaches. The most common tandem architectures employ a transparent conductive oxide (TCO) front electrode. Due to its fast deposition and up-scalability, sputter deposition is the preferred method for TCO deposition. The sensitive layers of perovskite solar cells are protected from sputter damage by a thermal atomic layer (ALD) deposited tin oxide (SnO2) buffer layer, which induces parasitic ab-sorption. Here, we propose a method to reveal the impact of sputter damage on SnO2 buffer layer-free devices. By performing light intensity-dependent current density-voltage (J-V) measurements and thereby reconstructing the single-junction solar cell pseudo J-V characteristics, we could associate sputter damage with trap-assisted non-radiative recombination losses. Additionally, we demonstrate a simple method to minimize sputter damage to the perovskite solar cell to the point where a protective SnO2 buffer layer is no longer required. By lowering the sputter power density during the TCO deposition, we regained-13 mV open-circuit voltage and-3% fill factor of the devices, improving the efficiency from 13.55 to 14.17%. We show that these improvements are linked to a reduction of transport and non-radiative recombination losses. Finally, we fabricated optically superior and sputter damage-free monolithic perovskite/silicon tandem devices without needing a protective SnO2 buffer layer. By doing so, we increased the tandem device current density by 0.52 mA/cm2, representing a crucial step toward further optimizing the optical performance of tandem devices.

All-perovskite tandem solar cells show great potential to enable the highest performance at reasonable costs for a viable market entry in the near future. In particular, wide-bandgap (WBG) perovskites with higher open-circuit voltage ( V OC ) are essential to further improve the tandem solar cells’ performance. Here, a new 1.8 eV bandgap triple-halide perovskite composition in conjunction with a piperazinium iodide (PI) surface treatment is developed. With structural analysis, it is found that the PI modifies the surface through a reduction of excess lead iodide in the perovskite and additionally penetrates the bulk. Constant light-induced magneto-transport measurements are applied to separately resolve charge carrier properties of electrons and holes. These measurements reveal a reduced deep trap state density, and improved steady-state carrier lifetime (factor 2.6) and diffusion lengths (factor 1.6). As a result, WBG PSCs achieve 1.36 V V OC , reaching 90% of the radiative limit. Combined with a 1.26 eV narrow bandgap (NBG) perovskite with a rubidium iodide additive, this enables a tandem cell with a certified scan efficiency of 27.5%.

Combining a perovskite top cell with a conventional passivated emitter and rear cell (PERC) silicon bottom cell in a monolithically integrated tandem device is an economically attractive solution to boost the power conversion efficiency (PCE) of silicon single‐junction technology. Proof‐of‐concept perovskite/silicon tandem solar cells using high‐temperature stable bottom cells featuring a polycrystalline silicon on oxide (POLO) front junction and a PERC‐type passivated rear side with local aluminum‐p+ contacts are reported. For this PERC/POLO cell, a process flow that is compatible with industrial, mainstream PERC technology is implemented. Top and bottom cells are connected via a tin‐doped indium oxide recombination layer. The recombination layer formation on the POLO front junction of the bottom cell is optimized by postdeposition annealing and mitigation of sputter damage. The perovskite top cell is monolithically integrated in a p−i−n junction device architecture. Proof‐of‐concept tandem cells demonstrate a PCE of up to 21.3%. Based on the experimental findings and supporting optical simulations, major performance enhancements by process and layer optimization are identified and a PCE potential of 29.5% for these perovskite/silicon tandem solar cells with PERC‐like bottom cell technology is estimated.

Perovskite–silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite–silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.

up to 150 words, unreferenced Perovskite/silicon tandem solar cells allow to overcome the power conversion efficiency limit of market-dominating silicon solar cells. So far, various textured tandem devices were presented aiming at improved optical performance, but highest efficiencies were still realized on polished silicon wafer cells enabling superior perovskite layer properties. Here we present perovskite/silicon tandem solar cells with gentle periodic nanotextures which feature various advantages without compromising the material quality of solution-processed perovskite layers. Reflection losses are reduced in comparison to planar tandems and the devices are less sensitive upon deviations from optimum layer thicknesses. The nanotextures also enable excellent perovskite film formation and a greatly increased fabrication yield. The open-circuit voltage improved by about 15 mV due to enhanced electronic properties of the perovskite top cell. In addition, an optically advanced rear reflector with a dielectric buffer layer reduced parasitic absorption at near-infrared wavelengths. Altogether, the improvements enabled a certified power conversion efficiency of 29.80%. Monolithic, 2-terminal perovskite/silicon tandem solar cells (PSTSC) have recently achieved power conversion efficiencies (PCE) exceeding 29% and therefore overcome the physical limit of market-dominating crystalline-silicon single-junction solar cells. Such high PCEs were reached by continuous improvements of the optical and electronic properties of PSTSC. These improvements include, amongst others, switching the cell polarity for enhanced top-contact transmission, and fine-tuning of various layers to improve the optical performance. In addition, various publications addressed the improvement of the electronic properties by optimizing contact layers, utilizing additives and adjusting the perovskite composition or deposition. Numerical studies predict a further increase of PCE with adequate light management by introducing textured device interfaces. For silicon solar cells, potassiumhydroxide etched random pyramidal textures with a size of several micrometers are commonly used for light management. However, they are not compatible with solutionprocessed perovskite absorbers without further adaptation. In recent years, different approaches to implement light management textures in PSTSC were investigated, either by adapting the perovskite deposition technique but leaving the pyramidal texture unchanged 20 with maximum PCE of 27.4%, or by adapting the pyramidal textures such that perovskite solution-processing becomes feasible leading to a maximum PCE of 28.6% (Fig. S1). These reported PCEs are still below the best scientifically published result for PSTSCs based on perovskite absorbers spin-coated onto silicon bottom cells with flat, polished front side (29.15%), mainly due to deficits of the perovskite material quality on standard and adapted pyramidal textures. Therefore, it remains a significant challenge to develop an appropriate texture, which is able to balance the persistent trade-off between electronic and optical performance of textured PSTSCs and hence allows to push the PCE beyond 30%. In recent studies we already introduced gentle sinusoidal nanotextures with sub-micrometer feature size (see Fig. 1d) as promising candidate for PSTSCs: optical simulations indicated that the PCE can be significantly enhanced compared to planar reference tandem solar cells. We further demonstrated experimentally that such nanotextures provide a feasible light-management solution in both, perovskite and silicon single junction solar cells, without compromising the optoelectronic quality of the respective absorber. In this work, we present PSTSCs with a gentle sinusoidal nanotexture connecting the advantages of structuring the silicon surface while preserving the material quality of the perovskite. We show that the nanotextured devices feature a substantial reduction of reflection losses compared to their planar counterpart and a significantly reduced sensitivity against deviations from optically optimum layer thicknesses. More than that, nanotexturing strongly improves the fabrication yield enabled by the excellent film formation properties of spin-coated perovskite films on nanotextured silicon bottom cells and a statistically relevant increase of the open-circuit voltage by 15 mV is observed. In order to meet the challenge of parasitic absorption losses, we further implement a reflector with dielectric buffer layer (RDBL) at the rear side of the silicon bottom cell. This buffer layer optically decouples the contact metal and the silicon absorber, allows to decrease the thickness of the transparent conductive layer and hence reduces parasitic absorption losses considerably. Combining both approaches, i.e. the gentle nanotexture at the front side and the reflector with dielectric buffer layer at the rear side of the silicon bottom cell, we demonstrate a monolithic PSTSC with an independently certified power conversion efficiency of 29.80%.

We present a monolithic two-terminal perovskite/ silicon tandem solar cell based on an industrial silicon bottom cell fabricated with mass-production-feasible processes. The solar cell exhibited a steady-state power conversion efficiency of 28.7% and an open-circuit voltage of over 1.9 V.

We report on proof-of-concept perovskite/silicon tandem solar cells on bottom cells featuring a polycrystalline silicon on oxide (POLO) front junction and a PERC-type passivated rear side with local aluminium-p+ contacts. We implement a process flow which is compatible with industrial, mainstream PERC technology. The top and bottom cells are connected via an indium tin oxide (ITO) layer, and the perovskite top cell is then monolithically integrated in a p-i-n architecture. The tunnel recombination junction between the two sub-cells, as well as the perovskite top cell are adapted from high efficiency perovskite/silicon heterojunction-based tandems. For the perovskite absorber layer, we use a mixed cation, mixed halide perovskite with a band gap of 1.68 eV. The proof-of-concept tandem cells demonstrate a power conversion efficiency (PCE) of 21.3%. We identify a potential for major performance enhancements by process and layer optimizations. Supported by optical simulations, we estimate a PCE potential of 29.5% for this tandem stack based on POLO/PERC bottom cells. Thus, we demonstrate that the large technology base of p-type PERC production has significant potential for an upgrade to highly efficient perovskite/POLO/PERC tandem solar cells.

We present results on perovskite/silicon tandem solar cells with almost 30% power conversion efficiency. They comprise sinusoidal nanotextures between top and bottom cells and optically advanced rear reflectors with a dielectric buffer layer.

Abstract Perovskite/silicon tandem solar cells allow to overcome the power conversion efficiency limit of market-dominating silicon solar cells. So far, various textured tandem devices were presented aiming at improved optical performance, but highest efficiencies were still realized on polished silicon wafer cells enabling superior perovskite layer properties. Here we present perovskite/silicon tandem solar cells with gentle periodic nanotextures which feature various advantages without compromising the material quality of solution-processed perovskite layers. Reflection losses are reduced in comparison to planar tandems and the devices are less sensitive upon deviations from optimum layer thicknesses. The nanotextures also enable excellent perovskite film formation and a greatly increased fabrication yield. The open-circuit voltage improved by about 15 mV due to enhanced electronic properties of the perovskite top cell. In addition, an optically advanced rear reflector with a dielectric buffer layer reduced parasitic absorption at near-infrared wavelengths. Altogether, the improvements enabled a certified power conversion efficiency of 29.80%.

In this work, we demonstrate how the use of a poly(ionic liquid) interlayer in combination with perovskite solar cells provides a bi-functionality of the surface allowing to concomitantly reduce the energy losses, enhance the charge extraction and improve the device stability all at once.

Monolithic perovskite/silicon tandem solar cells recently surpass the efficiency of silicon single‐junction solar cells. Most tandem cells utilize >250 μm thick, planarized float‐zone (FZ) silicon, which is not compatible with commercial production using <200 μm thick Czochralski (CZ) silicon. The perovskite/silicon tandem cells based on industrially relevant 100 μm thick CZ‐silicon without mechanical planarization are demonstrated. The best power conversion efficiency (PCE) of 27.9% is only marginally below the 28.2% reference value obtained on the commonly used front‐side polished FZ‐Si, which are about three times thicker. With both wafer types showing the same median PCE of 27.8%, the thin CZ‐Si‐based devices are preferred for economic reasons. To investigate perspectives for improved current matching and, therefore, further efficiency improvement, optical simulations with planar and textured silicon have been conducted: the perovskite's bandgap needs to be increased by ≈0.02 eV when reducing the silicon thickness from 280 to 100 μm. The need for bandgap enlargement has a strong impact on future tandem developments ensuring photostable compositions with lossless interfaces at bandgaps around or above 1.7 eV.

Through the optimization of the perovskite precursor composition and interfaces to selective contacts, we achieved a p-i-n-type perovskite solar cell (PSC) with a 22.3% power conversion efficiency (PCE). This is a new performance record for a PSC with an absorber bandgap of 1.63 eV. We demonstrate that the high device performance originates from a synergy between (1) an improved perovskite absorber quality when introducing formamidinium chloride (FACl) as an additive in the "triple cation" Cs0.05FA0.79MA0.16PbBr0.51I2.49 (Cs-MAFA) perovskite precursor ink, (2) an increased open-circuit voltage, VOC, due to reduced recombination losses when using a lithium fluoride (LiF) interfacial buffer layer, and (3) high-quality hole-selective contacts with a self-assembled monolayer (SAM) of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) on ITO electrodes. While all devices exhibit a high performance after fabrication, as determined from current-density voltage, J-V, measurements, substantial differences in device performance become apparent when considering longer-term stability data. A reduced long-term stability of devices with the introduction of a LiF interlayer is compensated for by using FACl as an additive in the metal-halide perovskite thin-film deposition. Optimized devices maintained about 80% of the initial average PCE during maximum power point (MPP) tracking for >700 h. We scaled the optimized device architecture to larger areas and achieved fully laser patterned series-interconnected mini-modules with a PCE of 19.4% for a 2.2 cm2 active area. A robust device architecture and reproducible deposition methods are fundamental for high performance and stable large-area single junction and tandem modules based on PSCs.